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Volume 26 Issue 5
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A Hierarchy of New Nonlinear Evolution Equations Associated with a 3×3 Matrix Spectral Problem
GENG Xian-Guo, LI Fang
Chin. Phys. Lett. 2009, 26 (5): 050201 .   DOI: 10.1088/0256-307X/26/5/050201
Abstract   PDF(pc) (204KB) ( 653 )
A 3×3 matrix spectral problem with three potentials and the corresponding hierarchy of new nonlinear evolution equations are proposed. Generalized Hamiltonian structures for the hierarchy of nonlinear evolution equations are derived with the aid of trace identity.
Group Classification and Exact Solutions of a Class of Variable Coefficient Nonlinear Wave Equations
HUANG Ding-Jiang, MEI Jian-Qin, ZHANG Hong-Qing
Chin. Phys. Lett. 2009, 26 (5): 050202 .   DOI: 10.1088/0256-307X/26/5/050202
Abstract   PDF(pc) (262KB) ( 642 )
Complete group classification of a class of variable coefficient (1+1)-dimensional wave equations is performed. The possible additional equivalence transformations between equations from the class under consideration and the conditional equivalence groups are also investigated. These allow simplification of the results of the classification and further applications of them. The derived Lie symmetries are used to construct exact solutions of special forms of these equations via the classical Lie method. Nonclassical symmetries of the wave equations are discussed.
Quasi-Hamiltonian Structure Associated with an Integrable Coupling System
LUO Lin, FAN En-Gui
Chin. Phys. Lett. 2009, 26 (5): 050203 .   DOI: 10.1088/0256-307X/26/5/050203
Abstract   PDF(pc) (199KB) ( 449 )
Starting from a spectral problem, a corresponding soliton hierarchy is proposed, and we construct an integrable coupling system with five dependent variables for the hierarchy by using a class of semi-direct sums of Lie algebras. Moreover, it is shown that the coupling system possesses quasi-Hamiltionian structures, and that infinitely many conserved quantities are obtained.
Effect of Quantum Point Contact Measurement on Electron Spin State in Quantum Dots
ZHU Fei-Yun, TU Tao, HAO Xiao-Jie, GUO Guang-Can, GUO Guo-Ping
Chin. Phys. Lett. 2009, 26 (5): 050301 .   DOI: 10.1088/0256-307X/26/5/050301
Abstract   PDF(pc) (307KB) ( 448 )
We study the time evolution of two electron spin states in a double quantum-dot system, which includes a nearby quantum point contact (QPC) as a measurement device. We find that the QPC measurement induced decoherence is in the micrsecond timescale. We also find that the enhanced QPC measurement will trap the system in its initial spin states, which is consistent with the quantum Zeno effect.
Radiative Energy Shifts of an Atom Coupled to the Derivative of a Scalar Field near a Reflecting Boundary
LI Cheng-Gai, YU Hong-Wei
Chin. Phys. Lett. 2009, 26 (5): 050401 .   DOI: 10.1088/0256-307X/26/5/050401
Abstract   PDF(pc) (229KB) ( 351 )
We study the radiative energy level shifts of a two-level atom in dipole coupling to the derivative of a massless scalar quantum field in a spacetime with a perfectly reflecting boundary, and calculate the contributions of vacuum fluctuations and radiation reaction to the level shift. It is found that the energy level shift of the excited state is an oscillating function of the atom's distance from the boundary and it can either be positive or negative, while that of the ground state is always positive. The most remarkable feature is that the energy level shift of the ground state behaves like 1/z4 when the atom's distance from the boundary, z, is very large as compared to the transition wavelength of the atom, while it behaves like 1/z3 when z is very small.
Phase and Polarization State of High-Frequency Relic Gravitational Waves
LI Fang-Yu, YANG Nan
Chin. Phys. Lett. 2009, 26 (5): 050402 .   DOI: 10.1088/0256-307X/26/5/050402
Abstract   PDF(pc) (205KB) ( 377 )
The displaying condition of strength, phase and polarization states of high-frequency relic gravitational waves (HFRGWs) in electromagnetic (EM) detecting systems is studied. It is shown that the displaying condition depends not only on the sensitivity of EM detecting systems and the amplitudes of HFRGWs, but also on the phase, the polarization states of HFRGWs and their matching to the EM detecting systems. In order to display simultaneously the strength, phase and polarization states of the resonant ``monochromatic component'' of HFRGWs, an important necessary condition is the utilization of two or more different EM detectors.
Increasing-order Projective Synchronization of Chaotic Systems with Time Delay
MIAO Qing-Ying, FANG Jian-An, TANG Yang, DONG Ai-Hua
Chin. Phys. Lett. 2009, 26 (5): 050501 .   DOI: 10.1088/0256-307X/26/5/050501
Abstract   PDF(pc) (272KB) ( 462 )
This work is concerned with lag projective synchronization of chaotic systems with increasing order. The systems under consideration have unknown parameters and different structures. Combining the adaptive control method and feedback control technique, we design a suitable controller and parameter update law to achieve lag synchronization of chaotic systems with increasing order. The result is rigorously proved by the Lyapunov stability theorem. Moreover, corresponding simulation results are given to verify the effectiveness of the proposed methods.
State-to-State Transitions in a Hindmarsh-Rose Neuron System
HUANG Shou-Fang, ZHANG Ji-Qian, DING Shi-Jiang
Chin. Phys. Lett. 2009, 26 (5): 050502 .   DOI: 10.1088/0256-307X/26/5/050502
Abstract   PDF(pc) (377KB) ( 464 )
We investigate the dynamical response of the neuron system to a feeble external signal by using the Hindmarsh-Rose model, when the system is tuned below the first bifurcation point, which corresponds to the period-1 bursting state, and an external signal with a fixed period of about 170s is introduced to the system. It is found that to respond to the outside signal, the system changes from the period-1 state to a period-2 one with variation of the signal amplitude, indicating the occurrence of state-to-state transition (SST). Moreover, when a signal with different fixed periods is introduced, we can also find a similar transition between other states. Furthermore, the effect of the frequency of the signal on the transition is also discussed. These results may imply that SST plays a constructive role in information processing in neuron systems.
A Novel Adaptive Observer-Based Control Scheme for Synchronization and Suppression of a Class of Uncertain Chaotic Systems
WANG Jing, TAN Zhen-Yu, MA Xi-Kui, GAO Jin-Feng
Chin. Phys. Lett. 2009, 26 (5): 050503 .   DOI: 10.1088/0256-307X/26/5/050503
Abstract   PDF(pc) (317KB) ( 563 )
A novel adaptive observer-based control scheme is presented for synchronization and suppression of a class of uncertain chaotic system. First, an adaptive observer based on an orthogonal neural network is designed. Subsequently, the sliding mode controllers via the proposed adaptive observer are proposed for synchronization and suppression of the uncertain chaotic systems. Theoretical analysis and numerical simulation show the effectiveness of the proposed scheme.
Anti-Control of Hopf Bifurcation in the Chaotic Liu System with Symbolic Computation
LÜ, Zhuo-Sheng, DUAN Li-Xia
Chin. Phys. Lett. 2009, 26 (5): 050504 .   DOI: 10.1088/0256-307X/26/5/050504
Abstract   PDF(pc) (199KB) ( 518 )
The anti-control of bifurcation refers to the task of creating a certain bifurcation with particular desired properties and location by appropriate controls. We consider, via feedback control and symbolic computation, the problem of anti-control of Hopf bifurcation in the chaotic Liu system. We propose an anti-control scheme and show that compared with the uncontrolled system, the anti-controlled Liu system can exhibit Hopf bifurcation in a much larger parameter region. The anti-control strategy used keeps the equilibrium structure of the Liu system and can be applied to generate Hopf bifurcation at the desired location with preferred stability. We illustrate the efficiency of the anti-control approach under different operating
Helicity Amplitude Analysis of e+e-→ψ(2S) →γχcJ→γΛ-Λ→γ pπ--+
LIAO Guang-Rui, PING Rong-Gang, YANG Yong-Xu
Chin. Phys. Lett. 2009, 26 (5): 051101 .   DOI: 10.1088/0256-307X/26/5/051101
Abstract   PDF(pc) (248KB) ( 423 )
An analysis of the helicity amplitude is performed on the process e+e-→ψ(2S) →γχcJ→γΛ-Λ→γ pπ--+. The joint angular distributions for each decay chain are given, and we focus on discussing the E1 contributions to ψ(2S) radiative decays, and the violation of the helicity selection rule in χcJ decays into hyperon pairs, together with the possibility of observing parity violation in successive hyperon decays.
Description of 178Hfm2 in the Constrained Relativistic Mean Field Theory
ZHANG Wei, PENG Jing, ZHANG Shuang-Quan
Chin. Phys. Lett. 2009, 26 (5): 052101 .   DOI: 10.1088/0256-307X/26/5/052101
Abstract   PDF(pc) (260KB) ( 357 )
Properties of the ground state of 178Hf and the isomeric state 178Hfm2 are studied within the adiabatic and diabatic constrained relativistic mean field (RMF) approaches. The RMF calculations reproduce well the binding energy and the deformation for the ground state of 178Hf. Using the ground state single-particle eigenvalues obtained in the present calculation, the lowest excitation configuration with Kπ=16+ is found to be ν(7/2-[514])-1(9/2+[624])1 π(7/2+[404])-1(9/2[514])1. Its excitation energy calculated by the RMF theory with time-odd fields taken into account is equal to 2.801MeV, i.e., close to the 178Hfm2 experimental excitation energy 2.446MeV. The self-consistent procedure accounting for the time-odd component of the meson fields is the most important aspect of the present calculation.
Coupling Parameter in the Single-j Shell Model
WANG Shou-Yu, Qi Bin, ZHANG Shuang-Quan,
Chin. Phys. Lett. 2009, 26 (5): 052102 .   DOI: 10.1088/0256-307X/26/5/052102
Abstract   PDF(pc) (321KB) ( 536 )
We propose a modified formula which is used to determine the coupling parameter C in the Hamiltonian of the single-j shell. In comparison with the previously known formula, the new formula improves the agreement between the intruder single-j levels and the Nilsson ones. For studies of chiral bands within the particle rotor model, the new coupling parameter will considerably influence the energy splitting between the doublet bands.
Relativistic Quasiparticle Random Phase Approximation with a Separable Pairing Force
TIAN Yuan, MA Zhong-Yu, Ring Peter
Chin. Phys. Lett. 2009, 26 (5): 052103 .   DOI: 10.1088/0256-307X/26/5/052103
Abstract   PDF(pc) (275KB) ( 367 )
In our previous work [Phys. Lett. (to be published), Chin. Phys. Lett. 23(2006)3226], we introduced a separable pairing force for relativistic Hartree-Bogoliubov calculations. This force was adjusted to reproduce the pairing properties of the Gogny force in nuclear matter. By using the well known techniques of Talmi and Moshinsky it can be expanded in a series of separable terms and converges quickly after a few terms. It was found that the pairing properties can be depicted on almost the same footing as the original pairing interaction, not only in nuclear matter, but also in finite nuclei. In this study, we construct a relativistic quasiparticle random phase approximation (RQRPA) with this separable pairing interaction and calculate the excitation energies of the first excited 2+ states and reduced B(E2;0+→2+) transition rates for a chain of Sn isotopes in RQRPA. Compared with the results of the full Gogny force, we find that this simple separable pairing interaction can describe the pairing properties of the excited vibrational states as well as the original pairing interaction.
Disentangling the Effects of Thickness of the Neutron Skin and Symmetry Potential in Nucleon Induced Reactions on Sn Isotopes
OU Li, LI Zhu-Xia, WU Xi-Zhen, SUN Wei-Li
Chin. Phys. Lett. 2009, 26 (5): 052501 .   DOI: 10.1088/0256-307X/26/5/052501
Abstract   PDF(pc) (439KB) ( 367 )
The effects of density dependence of symmetry energy and the thickness of the neutron skin in proton (neutron) induced reactions on Sn isotopes are investigated by means of the improved molecular dynamics model. The investigation shows that the target size dependence of the reaction cross sections for proton induced reactions on Sn isotopes is sensitive to the density dependence of the symmetry energy and less sensitive to the thickness of the neutron skin of the target nuclei, but that, for neutron induced reactions on Sn isotopes, it is less sensitive to the density dependence of the symmetry energy and sensitive to the thickness of the neutron skin of the target nucleus.
Impact Parameter Dependence of the Double Neutron/Proton Ratio of Nucleon Emissions in Isotopic Reaction Systems
ZHANG Xun-Chao, LI Bao-An, CHEN Lie-Wen, YONG Gao-Chan
Chin. Phys. Lett. 2009, 26 (5): 052502 .   DOI: 10.1088/0256-307X/26/5/052502
Abstract   PDF(pc) (393KB) ( 412 )
Within the transport model IBUU04, we investigate the double neutron/proton ratio of free nucleons taken from two reaction systems using two Sn isotopes at a beam energy of 50MeV/nucleon and with impact parameters 2fm, 4fm and 8fm, respectively. It is found that the double neutron/proton ratio from peripheral collisions is more sensitive to the density dependence of the symmetry energy than those from mid-central and central collisions.
Atomic Layer Deposition of Al2O3 on H-Passivated GeSi: Initial Surface Reaction Pathways with H/GeSi(100)-2×1
SHI Yu, SUN Qing-Qing, DONG Lin, LIU Han, DING Shi-Jin, ZHANG Wei
Chin. Phys. Lett. 2009, 26 (5): 053101 .   DOI: 10.1088/0256-307X/26/5/053101
Abstract   PDF(pc) (426KB) ( 528 )
The reaction mechanisms of Al(CH3)3 (TMA) adsorption on H-passivated GeSi(100)-2×1 surface are investigated with density functional theory. The Si-Ge and Ge-Ge one-dimer cluster models are employed to represent the GeSi(100)-2×1 surface with different Ge compositions. For a Si-Ge dimer of a H-passivated SiGe surface, TMA adsorption on both Si-H* and Ge-H* sites is considered. The activation barrier of TMA with the Si-H* site (1.2eV) is higher than that of TMA with the Ge-H* site (0.91eV), which indicates that the reaction proceeds more slowly on the Si-H* site than on the Ge-H* site. In addition, adsorption of TMA is more energetically favorable on the Ge-Ge dimer than on the Si-Ge dimer of H-passivated SiGe.
Stereodynamics of the He+D2+→HeD++D Reaction on the PALMIERI Surface
KONG Hao, LIU Xin-Guo, XU Wen-Wu, ZHANG Qing-Gang
Chin. Phys. Lett. 2009, 26 (5): 053102 .   DOI: 10.1088/0256-307X/26/5/053102
Abstract   PDF(pc) (426KB) ( 378 )
Using the quasi-classical trajectory method, the product rotational polarization of the ion-molecule reaction He+D2+ has been calculated at different collision energies on the PALMIERI potential energy surface [Palmieri et al. Mol. Phys. 98 (2000) 1835]. The distribution angle between k and j', P(θr), the distribution of the dihedral angle P(Φr), and the angular distribution of product rotational vectors in the form of polar plots in θr and Φr are calculated. In addition, four polarization-dependent differential cross sections are also presented in the center-of-mass frame, respectively. The results indicate that the rotational polarization of the product HeD+ presents different characters for different collision energies. These discrepancies may be ascribed to the different collision energies and constructions of the potential energy surface.
A Theoretical Strategy to Generate an Isolated 80-Attosecond Pulse
GUO Fu-Ming, YANG Yu-Jun, JIN Ming-Xing, DING Da-Jun, ZHU Qi-Ren
Chin. Phys. Lett. 2009, 26 (5): 053201 .   DOI: 10.1088/0256-307X/26/5/053201
Abstract   PDF(pc) (413KB) ( 471 )
Using a linearly polarized, phase-stabilized 2.66-femtosecond driving pulse of 400nm central wavelength orthogonally combined with another linearly polarized long pulse of 800nm central wavelength irradiating jointly on the helium atom, we demonstrate theoretically the generation of a clean isolated 80-attosecond pulse in the spectral region of 93-155 electron volts in a two-dimensional model.
Generalized Pseudospectral Method for Solving the Time-Dependent Schrödinger Equation Involving the Coulomb Potential
ZENG Si-Liang, ZOU Shi-Yang, YAN Jun,
Chin. Phys. Lett. 2009, 26 (5): 053202 .   DOI: 10.1088/0256-307X/26/5/053202
Abstract   PDF(pc) (332KB) ( 694 )
We present an accurate and efficient generalized pseudospectral method for solving the time-dependent Schrödinger equation for atomic systems interacting with intense laser fields. In this method, the time propagation of the wave function is calculated using the well-known second-order split-operator method implemented by the numerically exact, fast transform between the grid and spectral representations. In the grid representation, the radial coordinate is discretized using the Coulomb wave discrete variable representation (CWDVR), and the angular dependence of the wave function is expanded in the Gauss-Legendre-Fourier grid. In the spectral representation, the wave function is expanded in terms of the eigenfunctions of the field-free zero-order Hamiltonian. Calculations on the high order harmonic generation and ionization dynamics of hydrogen atom in strong laser pulses are presented to demonstrate the accuracy and efficiency of the present method. This new algorithm will be found more computationally attractive than the close-coupled wave packet method using CWDVR and/or methods based on evenly spaced grids.
Relativistic Distorted-Wave Collision Strengths of Ni-, Cu- and Zn-like Au Ions
YANG Ning-Xuan, DONG Chen-Zhong, JIANG Jun
Chin. Phys. Lett. 2009, 26 (5): 053401 .   DOI: 10.1088/0256-307X/26/5/053401
Abstract   PDF(pc) (267KB) ( 383 )

Excitation energies and electron impact excitation strengths from the ground states of Ni-, Cu- and Zn-like Au ions are calculated. The collision strengths are computed by a 213-levels expansion for the Ni-like Au ion, 405-levels expansion for the Cu-like Au ion and 229-levels expansion for the Zn-like Au ion. Configuration interactions are taken into account for all levels included. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbits are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. Excellent agreement is found when the results are compared with previous calculations and recent measurements.

Anion Mass Spectrometry Study of Ion-Pair Photodissociation of CO2 in the XUV Energy 19.70-22.24eV
FENG Qiang, TIAN Shan-Xi, ZHAO Yu-Jie, LIU Fu-Yi, SHAN Xiao-Bin, SHENG Liu-Si
Chin. Phys. Lett. 2009, 26 (5): 053402 .   DOI: 10.1088/0256-307X/26/5/053402
Abstract   PDF(pc) (305KB) ( 407 )
We demonstrate anion mass spectrometry using the Hefei synchrotron radiation source to investigate the ion-pair dissociation processes of molecules. The efficiency curve of the O- anionic product via ion-pair dissociations of CO2 is recorded with tunable extreme vacuum ultraviolet photons (energy: 19.70-22.24eV) and compared with the spectrum available in the literature. The possible dynamics of CO2+hv →CO++O- in this energy range is discussed.
Identification of the Amplification Mechanism in the First Free-Electron Laser as Net Stimulated Free-Electron Two-Quantum Stark Emission
S. H. Kim
Chin. Phys. Lett. 2009, 26 (5): 054101 .   DOI: 10.1088/0256-307X/26/5/054101
Abstract   PDF(pc) (197KB) ( 393 )
We find that the electron phase with respect to the incident laser radiation must be random in the first free-electron laser (FEL) and, hence, the incident laser radiation works as a relaxation force to keep a Maxwellian distribution. We formulate the threshold laser intensity for amplification which agrees with the measured value in the order of magnitude in the first FEL. The magnetic wiggler must produce an electric wiggler whose period is the same as that of the magnetic wiggler. We find that net stimulated free-electron two-quantum Stark (FETQS) emission driven by this electric wiggler is the mechanism responsible for the measured gain and the measured laser intensity at the plateau in the first FEL.
Doping Defects in Two-Dimensional Holographic Photonic Crystals Using a Continuous-Wave Visible Laser
ZHAI Tian-Rui, REN Zhi, ZHAO Rong-Kuo, WANG Zhao-Na, WANG Li-Feng, ZHOU Jing, LIU Da-He
Chin. Phys. Lett. 2009, 26 (5): 054201 .   DOI: 10.1088/0256-307X/26/5/054201
Abstract   PDF(pc) (3308KB) ( 470 )
It is demonstrated that defects of any shape or size can be doped in holographic photonic crystals using a cw visible laser and spherical/cylindrical lens. Defects with different sizes at any depth in the material can be obtained by controlling the position of the focal point of the lens and exposure value. We facilitate the implementation of sub-wavelength arbitrary point or line defects in large-size 2D holographic photonic crystals
Extreme Ultraviolet Pulse Shaping with Aligned Molecules
ZENG Zhi-Nan, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2009, 26 (5): 054202 .   DOI: 10.1088/0256-307X/26/5/054202
Abstract   PDF(pc) (603KB) ( 414 )
We theoretically propose a simple scheme to shape the extreme ultraviolet pulse on the attosecond timescale with the aligned molecule. This may offer a new way to manipulate and control photon emission on the attosecond timescale.
Optical Switching in Silicon Nanowaveguide Ring Resonators Based on Kerr Effect and TPA Effect
LI Chun-Fei, DOU Na
Chin. Phys. Lett. 2009, 26 (5): 054203 .   DOI: 10.1088/0256-307X/26/5/054203
Abstract   PDF(pc) (246KB) ( 649 )
We analyze theoretically the 1×2 low-power all-optical switching in silicon nanowaveguide ring resonators (RR) based on the Kerr effect and two-photon absorption (TPA), and give a comparison between both the all-optical switches. The calculation shows that the switching power of the TPA-RR switch is 3 orders smaller than that of the Kerr-RR switch. The switching time for both the switches is about 100ps.
Design of Nearly Zero Dispersion Flattened Photonic Crystal Fiber with Double Cladding
WANG Wei, HOU Lan-Tian, SONG Jun-Jie, ZHOU Gui-Yao,
Chin. Phys. Lett. 2009, 26 (5): 054204 .   DOI: 10.1088/0256-307X/26/5/054204
Abstract   PDF(pc) (388KB) ( 822 )
A novel design of nearly zero dispersion flattened photonic crystal fiber (PCF) with double cladding is proposed. To employ traditional stack and draw technology, the cladding is composed of a traditional triangular lattice of air-holes and silica. The dispersion of the fiber is mainly engineered by the small air holes in the inner cladding, which are easily preserved in the fiber drawing procedure. The large air-holes in the outer cladding are mainly for light confinement. Thus, the dispersion property of the PCF is insensitive to the deformation of the air holes in the outer cladding. Using 8 layers of air-hole ring, the loss of the fundamental mode for the PCF is as low as 0.13dB/km at 1.55μm. The dispersion of the PCF fluctuates from -0.023 to 0.021ps・km-1nm-1 in the range 1.45-1.625μm.
Effects of Different Zernike Terms on Optical Quality and Vision of Human Eyes
ZHAO Hao-Xin, XU Bing, LI Jing, DAI Yun, YU Xiang, ZHANG Yu-Dong, JIANG Wen-Han
Chin. Phys. Lett. 2009, 26 (5): 054205 .   DOI: 10.1088/0256-307X/26/5/054205
Abstract   PDF(pc) (305KB) ( 459 )
The visual quality of human eyes is much restricted by high-order aberrations as well as low-order aberrations (defocus and astigmatism), but each term of high-order aberrations contributes differently. The visual acuity and contrast of the image on the retina can be gained by inducing aberrations to each term of high orders. Based on an adaptive optics system, the visual acuity of four subjects is tested by inducing aberrations to each Zernike term after correcting all the aberrations of the subjects. Zernike terms near the center of the Zernike tree affect visual quality more than those near the edge both theoretically and experimentally, and 0.1-μm aberration of these terms can clearly degrade the optical quality and vision. The results suggest that correcting the terms near the center of Zernike tree can improve the visual quality effectively in practice.
Integratable and High Speed Complex-Coupled MQW-DFB Lasers Fabricated on Semi-Insulating Substrates
CHENG Yuan-Bing, WANG Yang, SUN Yu, PAN Jiao-Qing, BIAN Jing, AN Xin, ZHAO ling-juan, WANG Wei
Chin. Phys. Lett. 2009, 26 (5): 054206 .   DOI: 10.1088/0256-307X/26/5/054206
Abstract   PDF(pc) (510KB) ( 664 )
A novel integratable and high speed InGaAsP multi-quantum well (MQW) complex-coupled distributed feedback (DFB) laser is successfully fabricated on a semi-insulating substrate. The fabricated ridge DFB laser exhibits a threshold current of 26mA, a slope efficiency of 0.14W・A-1 and a side mode suppression ratio of 40dB together with a 3dB bandwidth of more than 8GHz. The device is suitable for 10Gbit/s optical fiber communication.
Morphology Dependence of Power Spectra for Different Polarized States from Two-Dimensional Active Random Media
LIU Hai, LIU Jin-Song, LÜ, Jian-Tao, WANG Ke-Jia
Chin. Phys. Lett. 2009, 26 (5): 054207 .   DOI: 10.1088/0256-307X/26/5/054207
Abstract   PDF(pc) (481KB) ( 409 )
Spectra for two polarized states with competition on the inverted population in a set of two-dimensional (2D) active random media are calculated, and these random media have the same random constitution but different shapes. Results show that the power spectra for the two polarized states are all morphology dependent in the competition. The appropriate design of the shapes has an obvious effect on the selection of TM polarized modes and can improve the adverse situation of the TM polarized state in the competition. Such a property presents a new mode-selecting technique for each polarized mode in random media.
Generation of 170-fs Laser Pulses at 1053nm by a Passively Mode-Locked Yb:YAG Laser
ZHOU Bin-Bin, WEI Zhi-Yi, LI De-Hua, TENG Hao, Bourdet G. L.
Chin. Phys. Lett. 2009, 26 (5): 054208 .   DOI: 10.1088/0256-307X/26/5/054208
Abstract   PDF(pc) (284KB) ( 446 )
A novel method is developed to obtain 1.05μm laser operation with a Yb:YAG laser. By using a Yb:YAG crystal with proper length and doping concentration, a femtosecond Yb:YAG laser is realized at the central wavelength of 1053nm. The measured pulse duration and spectral bandwidth (FWHM) are 170fs and 7nm; the repetition rate is 80MHz. Under a power pump of 2W, an average mode-locking power of 180mW is achieved.
Investigation of Ag2O Thermal Decomposition by Terahertz Time-Domain Spectroscopy
Chin. Phys. Lett. 2009, 26 (5): 054209 .   DOI: 10.1088/0256-307X/26/5/054209
Abstract   PDF(pc) (986KB) ( 571 )
Application of terahertz time-domain spectroscopy is demonstrated to study the process of Ag2O thermal decomposition. In the process of decomposition, the time-resolved signals are characterized by broad oscillations and decreased intensity, and THz pulse essentially contains two broad spectral components: one centered at around 0.35THz and a band with a maximum at around 0.81THz shift to 0.71THz. Optical absorption spectra of different specimens are studied in the frequency range 0.3-1.4THz and the data are analyzed by the relevant theory of the effective medium approach combined with the Drude-Lorentz model. The analysis suggests that optical properties stem from the Drude term for the metallic phase and the Lorentz term for the insulator phase in the complex system.
SiO2 Waveguide Resonator Used in an Integrated Optical Gyroscope
YU Huai-Yong, ZHANG Chun-Xi, FENG Li-Shuang, ZHOU Zhen, HONG Ling-Fei
Chin. Phys. Lett. 2009, 26 (5): 054210 .   DOI: 10.1088/0256-307X/26/5/054210
Abstract   PDF(pc) (606KB) ( 1166 )
An integrated optical waveguide resonator based on a SiO2 waveguide is proposed, fabricated and tested. The method of designing the resonator is also presented. The optimal splitting ratio of the coupler is gained by simulating the relationship between the splitting ratio of the key coupler in the resonator and the resonator's finesse with resonance depth. The calculated fundamental detection limit of this integrated optical waveguide resonator is 1.6°/h. Finally, a micro-optical gyroscope system based on the integrated waveguide resonator is built, and the measured resonator's finesse F is close to 70 under fluctuating temperature. To the best of our knowledge, the present F is the best result to date. For the coupler splitting rate the experimental results have fixed errors with the simulation results caused by fabrication processes which can be easily eliminated, implying that the method of design is effective and applicable.
Comparison of Nd:YAG Ceramic Laser Pumped at 885nm and 808nm
ZONG Nan, ZHANG Xiao-Fu, MA Qing-Lei, WANG Bao-Shan, CUI Da-Fu, PENG Qin-Jun, XU Zu-Yan, PAN Yu-Bai, FENG Xi-Qi
Chin. Phys. Lett. 2009, 26 (5): 054211 .   DOI: 10.1088/0256-307X/26/5/054211
Abstract   PDF(pc) (484KB) ( 1762 )
Laser performance of 1064nm domestic Nd:YAG ceramic lasers for 885nm direct pumping and 808nm traditional pumping are compared. Higher slope efficiency of 34% and maximum output power of 16.5W are obtained for the 885nm pump with a 6mm length 1at.% Nd:YAG ceramic. The advantages for 885nm direct pumping are discussed in detail. This pumping scheme for highly doping a Nd:YAG ceramic laser is considered as an available way to generate high power and good beam quality simultaneously.
Synchronization and Coherent Combining of Two Pulsed Fiber Ring Lasers Based on Direct Phase Modulation
WANG Xiao-Lin, ZHOU Pu, MA Hao-Tong, CHEN Zi-Lun, LI Xiao, XU Xiao-Jun, LIU Ze-Jin
Chin. Phys. Lett. 2009, 26 (5): 054212 .   DOI: 10.1088/0256-307X/26/5/054212
Abstract   PDF(pc) (701KB) ( 647 )
We demonstrate a scalable architecture for coherent combining of pulsed fiber ring lasers based on mutual injection and direct phase modulation. By direct phase modulation in the common arm of two ring lasers, synchronous pulsed lasers can be generated and coherent combining of the two synchronous lasers is obtained. Two pulsed fiber ring lasers are coherently combined with 0.55μJ pulse energy and 10μs pulse duration at a repetition rate of 27.5kHz. Experimental results show that the two fiber ring lasers are phase locked with an invariable phase difference of π and have good temporal synchronization and spatial coherence. The combining efficiency of the two pulsed fiber laser reaches 90% and the fringe contrast is larger than 40%. Neither active phase control nor polarization control is used in our experiment and this method can be extended to combine more beams and higher repetition rate scaling up to higher power.
Optical Transmission Spectra of Anodic Aluminum Oxide Membranes with a Dual Layer-by-Layer Structure
LING Zhi-Yuan, CHEN Shuo-Shuo, HU Xing, LI Yi
Chin. Phys. Lett. 2009, 26 (5): 054213 .   DOI: 10.1088/0256-307X/26/5/054213
Abstract   PDF(pc) (938KB) ( 674 )
By adjusting the anodization voltage periodically in the process of electrochemical oxidation of aluminum and subsequent chemical etching, anodic aluminum oxide membranes with a dual periodic layer-by-layer structure are prepared. Optical transmission spectra analyses prove that the dip position is dependent on the thickness of the layer and can be easily adjusted by the anodization voltage according to the Bragg-Snell formula. This result implies that the position and width of the stop band and the pass band in the visible and near infrared wavelength region can be designed and prepared arbitrarily. It is expected that these kinds of anodic aluminum oxide membranes may find applications in the fabrication of various optical devices.
Emissions of Photonic Crystal Waveguides with Discretely Modulated Surfaces
TANG Dong-Hua, CHEN Li-Xue, LIU Yan, SUN Xiu-Dong, DING Wei-Qiang
Chin. Phys. Lett. 2009, 26 (5): 054214 .   DOI: 10.1088/0256-307X/26/5/054214
Abstract   PDF(pc) (527KB) ( 356 )
Transmission properties of photonic crystal (PC) waveguides with discretely modulated exit surfaces are investigated numerically using the finite-difference time-domain (FDTD) method. Unlike the case of periodically modulated surfaces, where the transmission beam tends to be a single and directional beam, when the exit surfaces are modulated only at several discrete points, the emission power tends to split into multiple and directional beams. We explain this phenomenon using a multiple point source interference model. Based on these results, we propose a 1-to-Nbeam splitter, and numerically realized high efficiency coupling between a PC sub-wavelength waveguide and three traditional dielectric waveguides with a total efficiency larger than 92%. This simple, easy fabrication, and controllable mechanism may find more potential applications in integrated optical circuits.
A Diode-Side-Pumped Dynamic Fundamental Mode Nd:YAG Laser
MA Jian-Li, DUANMU Qing-Duo, WANG Guo-Zheng, HAO Yong-Qin, ZHONG Jiang-Chang
Chin. Phys. Lett. 2009, 26 (5): 054215 .   DOI: 10.1088/0256-307X/26/5/054215
Abstract   PDF(pc) (582KB) ( 496 )
A fundamental mode Nd:YAG laser is experimentally demonstrated with a stagger pumped laser module and a special resonator. The rod is pumped symmetrically by staggered bar modules. A dynamic fundamental mode is achieved with the special resonator under different pump levels. A maximal continuous wave output of 61W (M2=1.4) is achieved with a single rod. An average output of 47W, pulse width of 54ns, pulse energy of 4.7mJ and peak power of 87kW are obtained under the Q-switched operation of 10kHz.
Nonlinearity of InP-Doped Fibers
Chin. Phys. Lett. 2009, 26 (5): 054216 .   DOI: 10.1088/0256-307X/26/5/054216
Abstract   PDF(pc) (691KB) ( 458 )
By combining nano-technology with fiber technology, an optical fiber doped with semiconductor nano-particles as InP is fabricated by using the modified chemical vapor deposition (MCVD) method. Proved by experiment, the fiber has excellent waveguide characteristics, and the concentration of InP is approximately 0.1%. By using a scanning electron microscope, a stereo-scan photograph of the fiber is obtained, and based on the graph, presentations of the fiber under both magnetic and electronic fields are simulated, the effective core area Aeff ≈ 10μm2 is calculated, and so is the nonlinear index γ =10.53W-1/Km of the fiber. This research leads a new method of high nonlinearity fiber fabrication.
Ultrasonic Vibration Suspends Large Pendant Drops
HONG Zhen-Yu, XIE Wen-Jun, WEI Bing-Bo
Chin. Phys. Lett. 2009, 26 (5): 054301 .   DOI: 10.1088/0256-307X/26/5/054301
Abstract   PDF(pc) (377KB) ( 437 )
A stationary substrate can suspend only small pendant drops even with excellent wetting ability because of gravity. We report the suspension of large pendant water drops by a copper substrate that vibrates ultrasonically with a frequency of 22kHz. The mass of the largest pendant drop suspended
by the vibrating substrate reaches 1.1g, which is 9 times that by the same stationary substrate. The pendant drop deforms drastically and quickly at both the beginning and the end of the vibration procedure. As the vibration power increases, the contact area between the drop and substrate expands and the drop height shrinks accordingly. Theoretical analysis indicates that the Bernoulli pressure induced by ultrasonic vibration may contribute strongly to enhancing the suspensibility of pendant drops.
Exact Periodic Solitary Solutions to the Shallow Water Wave Equation
LI Dong-Long, ZHAO Jun-Xiao,
Chin. Phys. Lett. 2009, 26 (5): 054701 .   DOI: 10.1088/0256-307X/26/5/054701
Abstract   PDF(pc) (1987KB) ( 415 )
Exact solutions to the shallow wave equation are studied based on the idea of the extended homoclinic test and bilinear method. Some explicit solutions, such as the one soliton solution, the doubly-periodic wave solution and the periodic solitary wave solutions, are obtained. In addition, the properties of the solutions are investigated.
Investigation of an S-Band Tapered Magnetically Insulated Transmission Line Oscillator
LI Zhi-Qiang, ZHONG Hui-Huang, FAN Yu-Wei, SHU Ting, QIAN Bao-Liang, XU Liu-Rong, ZHAO Yan-Song
Chin. Phys. Lett. 2009, 26 (5): 055201 .   DOI: 10.1088/0256-307X/26/5/055201
Abstract   PDF(pc) (735KB) ( 796 )
We present an improved structure of the tapered magnetically insulated transmission line oscillator (MILO). Simulation results show that this structure can obtain more microwave power with higher efficiency. Studies indicate that the distance between the load support legs and the last vane can affect the operation characteristics of this device. In the experiments, we obtain microwave with peak power of 2GW, frequency of 2.63GHz, and mode TM01. The beam to microwave power efficiency is 11%.
The influence of Exciting Frequency on N2 and N2+ Vibrational Temperature of Nitrogen Capacitively Coupled Plasma
HUANG Xiao-Jiang, XIN Yu, ZHANG Jie, NING Zhao-Yuan
Chin. Phys. Lett. 2009, 26 (5): 055202 .   DOI: 10.1088/0256-307X/26/5/055202
Abstract   PDF(pc) (345KB) ( 642 )
By using optical emission spectroscopy (OES), N2 and N2+ vibrational temperatures in capacitively coupled plasma discharges with different exciting frequencies are investigated. The vibrational temperatures are acquired by comparing the measured and calculated spectra of selected transitions with a least-square procedure. It is found that N2 and N2+ vibrational temperatures almost increase linearly with increasing exciting frequency up to 23MHz, then increase slowly or even decrease. The pressure corresponding to the maximum point of N2 vibrational temperature decreases with the increasing exciting frequency. These experimental phenomena are attributed to the increasing electron density, whereas the electron temperature decreases with exciting frequency rising.
Orbital Relaxation Effects in the Calculation of Aluminum Kα Absorptions
JIN Feng-Tao, HUANG Tian-Xuan, DING Yong-Kun, ZHENG Zhi-Jian, YUAN Jian-Min
Chin. Phys. Lett. 2009, 26 (5): 055203 .   DOI: 10.1088/0256-307X/26/5/055203
Abstract   PDF(pc) (310KB) ( 418 )
A recent experimental Kα transmission spectrum of an aluminum plasma is theoretically studied by a detailed level accounting model. It is found that the orbital relaxation effects of the K- and L-shell orbitals should be considered to calculate accurate line positions and strengths. To do this the initial and the final radial wave functions of Kα lines are respectively optimized by solving the full relativistic Dirac-Fock equation. Extensive configuration interaction calculations are performed to obtain the energy levels and the oscillator strengths. It is shown that both the line positions and the line strengths agree quite well with experiment when the orbital relaxations are considered.
Electric Conductivity of Phosphorus Nanowires
ZHANG Jing-Xiang, LI Hui, ZHANG Xue-Qing, LIEW Kim-Meow
Chin. Phys. Lett. 2009, 26 (5): 056101 .   DOI: 10.1088/0256-307X/26/5/056101
Abstract   PDF(pc) (477KB) ( 386 )
We present the structures and electrical transport properties of nanowires made from different strands of phosphorus chains encapsulated in carbon nanotubes. Optimized by density function theory, our results indicate that the conductance spectra reveal an oscillation dependence on the size of wires. It can be seen from the density of states and current-voltage curves that the structure of nanowires affects their properties greatly. Among them, the DNA-like double-helical phosphorus nanowire exhibits the distinct characteristic of an approximately linear I-V relationship and has a higher conductance than others. The transport properties of phosphorus nanowires are highly correlated with their microstructures.
Controlled Evolution of Silicon Nanocone Arrays Induced by Ar+ Sputtering at Room Temperature
LI Qin-Tao, LI Zhi-Gang, XIE Qiao-Ling, GONG Jin-Long, ZHU De-Zhang
Chin. Phys. Lett. 2009, 26 (5): 056102 .   DOI: 10.1088/0256-307X/26/5/056102
Abstract   PDF(pc) (713KB) ( 778 )
Controlled evolution of silicon nanocone arrays induced by Ar+ sputtering at room temperature, using the coating carbon as a mask, is demonstrated. The investigation of scanning electron microscopy indicates that the morphology of silicon nanostructures can be controlled by adjusting the thickness of the coating carbon film. Increasing the thickness of the coating carbon film from 50-60nm, 250-300nm and 750-800nm to 1500nm, the morphologies of silicon nanostructures are transformed from smooth surface ripple, coarse surface ripple and surface ripple with densely distributed nanocones to nanocone arrays with a high density of about 1×109-2×109 cm-2.
Covering Rules and Nearest Neighbour Configurations of the Dodecagonal Quasiperiodic Structure
FU Hong, LIAO Long-Guang, FU Xiu-Jun
Chin. Phys. Lett. 2009, 26 (5): 056103 .   DOI: 10.1088/0256-307X/26/5/056103
Abstract   PDF(pc) (232KB) ( 503 )
A dodecagonal quasiperiodic structure can be generated by cluster covering and the quasilattice is described in terms of the quasi-unit cell. We study the structural properties of the two-dimensional dodecagonal quasilattice in the covering scheme. The pair covering rules and the nearest neighbour configurations are determined. It is shown that the dodecagonal structure is more complicated than those of decagonal and octagonal quasilattices.
Nonvolatile Memory Characteristics with Embedded High Density Ruthenium Nanocrystals
MAO Ping, ZHANG Zhi-Gang, PAN Li-Yang, XU Jun, CHEN Pei-Yi
Chin. Phys. Lett. 2009, 26 (5): 056104 .   DOI: 10.1088/0256-307X/26/5/056104
Abstract   PDF(pc) (588KB) ( 457 )
Ruthenium (Ru) nanocrystals (NCs) embedded in SiO2 gate stacks are formed by rapid thermal annealing for the whole gate stacks and embedded in the memory structure, which is compatible with conventional CMOS technology. The devices exhibit a substantial and clockwise hysteresis in capacitance-voltage measurement. The Ru NCs exhibit high density (2×1012cm-2), small size (2-4nm) and good uniformity both in spatial distribution and morphology. The charging and long-term retention performances are explained by the Coulomb Blockade phenomena and the asymmetric electron tunnel barrier between the Ru NCs and the Si substrate, respectively.
First-Principles Calculations of Elastic and Thermal Properties of Lanthanum Hexaboride
XU Guo-Liang, CHEN Jing-Dong, XIA Yao-Zheng, LIU Xue-Feng, LIU Yu-Fang, ZHANG Xian-Zhou
Chin. Phys. Lett. 2009, 26 (5): 056201 .   DOI: 10.1088/0256-307X/26/5/056201
Abstract   PDF(pc) (382KB) ( 1130 )
The plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to anaylse the bulk modulus, thermal expansion coefficient and heat capacity of LaB6. The quasi-harmonic Debye model, using a set of total energy versus
volume obtained with the plane-wave pseudopotential method, is applied to the study of the thermal properties and vibrational effects. We analyse the bulk modulus of LaB6 up to 1500K. The elastic properties calculations show that our system is mechanically stable. For the heat capacity and the thermal expansion, significant differences in properties are observed above 300K. The calculated zero pressure bulk modulus is in good agreement with the
experimental data. Moreover, the Debye temperatures are determined from the non-equilibrium Gibbs functions and compared to available data.
Influence of pH on Nanofluids' Viscosity and Thermal Conductivity
WANG Xian-Ju, LI Xin-Fang
Chin. Phys. Lett. 2009, 26 (5): 056601 .   DOI: 10.1088/0256-307X/26/5/056601
Abstract   PDF(pc) (341KB) ( 3125 )
Aiming at the dispersion stability of nanoparticles regarded as the guide of heat transfer enhancement, we investigate the viscosity and the thermal conductivity of Cu and Al2O3 nanoparticles in water under different pH values. The results show that there exists an optimal pH value for the lowest viscosity and the highest thermal conductivity, and that at the optimal pH value the nanofluids containing a small amount of nanoparticles have noticeably higher thermal conductivity than that of the base fluid without nanoparticles. For the two nanofluids the enhancements of thermal conductivity are observed up to 13% (Al2O3-water) or 15% (Cu-water) at 0.4wt%, respectively. Therefore, adjusting the pH values is suggested to improve the stability and the thermal conductivity for practical applications of nanofluid.
Growth-Parameter Spaces and Optical Properties of Cubic Boron Nitride Films on Si(001)
FAN Ya-Ming, ZHANG Xing-Wang, YOU Jing-Bi, YING Jie, TAN Hai-Ren, CHEN Nuo-Fu
Chin. Phys. Lett. 2009, 26 (5): 056801 .   DOI: 10.1088/0256-307X/26/5/056801
Abstract   PDF(pc) (389KB) ( 420 )
Cubic boron nitride (c-BN) films were deposited on Si(001) substrates in an ion beam assisted deposition (IBAD) system under various conditions, and the growth parameter spaces and optical properties of c-BN films have been investigated systematically. The results indicate that suitable ion bombardment is necessary for the growth of c-BN films, and a well defined parameter space can be established by using the P/a-parameter. The refractive index of BN films keeps a constant of 1.8 for the c-BN content lower than 50%, while for c-BN films with higher cubic phase the refractive index increases with the c-BN content from 1.8 at χc=50% to 2.1 at χc=90%. Furthermore, the relationship between n and ρ for BN films can be described by the Anderson-Schreiber equation, and the overlap field parameter γ is determined to be 2.05.
Effect of Molecular Interactions between the Solid Wall and Liquid on the Flow Properties in Microtubes
BAO Fu-Bing, LIN Jian-Zhong,
Chin. Phys. Lett. 2009, 26 (5): 056802 .   DOI: 10.1088/0256-307X/26/5/056802
Abstract   PDF(pc) (278KB) ( 433 )
The flow properties in microtubes, such as velocity profiles and pressure distributions, are different from those in macrotubes. We attribute this phenomenon to the molecular interactions between the solid wall and inner liquid. The apparent viscosity, which takes into consideration the molecular interactions, is introduced in the present study and the Navier-Stokes equations are solved. Water is adopted in the calculation. For the hydrophilic material wall, the water is more like to adhere to the wall. The velocity near the wall is smaller than that of conventional theory, while the centerline velocity and pressure gradients are much larger. Such a phenomenon becomes much more obvious with the decrease in tube diameter.
Oxygen Recovery in Hf Oxide Films Fabricated by Sputtering
JIANG Ran, LI Zi-Feng
Chin. Phys. Lett. 2009, 26 (5): 057101 .   DOI: 10.1088/0256-307X/26/5/057101
Abstract   PDF(pc) (411KB) ( 496 )
The chemical structure of ultrathin Hf oxide films (< 10nm) fabricated by a standard sputtering method is investigated using x-ray spectroscopy and Rutherford backscattering spectroscopy. According to the experiments, oxygen species are impacted to the HfO2/Si interface during the initial sputtering, and then released back to the upper HfO2 region driven by the oxygen concentration grads. A vacuum annealing can greatly enhance this recovery process. Additionally, significant SiO2 reduction in the interface is observed after the vacuum annealing for the thick HfO2 films in our experiment. It might be an effective method to confine the interfacial layer thickness by sputtering thick HfO2 in no-oxygen ambient.
Correlation between Zero-Field Splitting and Site Distortions of Cr3+ Ions in NH4Cl:Cr3+ System: a Complete Energy Matrix Study
GAO Ming-Liang, KUANG Xiao-Yu, ZHAO Ya-Ru, QI Lin, LI Yan-Fang
Chin. Phys. Lett. 2009, 26 (5): 057102 .   DOI: 10.1088/0256-307X/26/5/057102
Abstract   PDF(pc) (384KB) ( 435 )
A theoretical method for investigating the inter-relation between the electronic and molecular structures of 3d3 configuration ions in a tetragonal ligand field is established on the basis of the 120×120 complete energy matrices. Using this method, the local structure parameters of two tetragonal Cr3+ centers in the NH4Cl:Cr3+ system are determined. Furthermore, the relations between the molecular symmetry and the ligand field symmetry are discussed.
Acceptor Concentration Effects on Photovoltaic Response in the La1-xSrxMnO3/SrNbyTi1-yO3 Heterojunction
LIAO Leng, JIN Kui-Juan, HAN Peng, ZHANG Li-Li, LÜ, Hui-Bin, GE Chen
Chin. Phys. Lett. 2009, 26 (5): 057301 .   DOI: 10.1088/0256-307X/26/5/057301
Abstract   PDF(pc) (395KB) ( 398 )
Photovoltaic response in the heterojunction of La1-xSrxMnO3/SrNbyTi1-yO3 (LSMO/SNTO) is analyzed theoretically based on the drift-diffusion model. It is found that the decrease of acceptor concentration in the La1-xSrxMnO3 layer of heterojunction can increase the peak value of photovoltaic signal and the speed of photovoltaic response, whereas the changing of donor concentration in the SrNbyTi1-yO3 layer has no such evident effect. Furthermore, the result also indicates that the modulation of Sr doping in La1-xSrxMnO3 is an effective method to accommodate the sensitivity and the speed of photovoltaic response for LSMO/SNTO photoelectric devices.
All-Optical Modulation with a Surface Plasmon Mach-Zehnder Interferometer
WU Xiao-Fei, ZHANG Jia-Sen, LI Zhi, LIU Ying-Liang, GONG Qi-Huang
Chin. Phys. Lett. 2009, 26 (5): 057302 .   DOI: 10.1088/0256-307X/26/5/057302
Abstract   PDF(pc) (374KB) ( 484 )
We use two parallel nano-slits in a silver film to form a surface plasmon Mach-Zehnder interferometer (MZI), based on the interference of two surface plasmon waves propagating along the two surfaces of the silver film. Coating the silver film with a photoinduced birefringence polymer film, we achieve optical modulation of the MZI output by changing the refractive index of the polymer film with a pump beam. An on/off ratio of 2.7 is obtained for a probe wavelength of 865nm.
Hole Spin Relaxation in an Ultrathin InAs Monolayer
LI Tao, ZHU Yong-Gang, ZHANG Xin-Hui, MA Shan-Shan, WANG Peng-Fei, NIU Zhi-Chuan
Chin. Phys. Lett. 2009, 26 (5): 057303 .   DOI: 10.1088/0256-307X/26/5/057303
Abstract   PDF(pc) (367KB) ( 441 )
We investigate the spin relaxation time of holes in an ultrathin neutral InAs monolayer (1.5ML) and compare with that of electrons, using polarization-dependent time-resolved photoluminescence (TRPL) experiments. With excitation energies above the GaAs gap, we observe a rather slow relaxation of holes (τ1h= 196±17ps) that is in the magnitude similar to electrons (τ1e=354±32ps) in this ultrathin sample. The results are in good agreement with earlier theoretical prediction, and the phonon scattering due to spin-orbit coupling is realized to play a dominant role in the carrier spin kinetics.
Inter-Layer Energy Transfer through Wetting-Layer States in Bi-layer InGaAs/GaAs Quantum-Dot Structures with Thick Barriers
XU Zhang-Cheng, ZHANG Ya-Ting, Jø, rn M. Hvam, Yoshiji Horikoshi
Chin. Phys. Lett. 2009, 26 (5): 057304 .   DOI: 10.1088/0256-307X/26/5/057304
Abstract   PDF(pc) (364KB) ( 380 )
The inter-layer energy transfer in a bi-layer InGaAs/GaAs quantum dot structure with a thick GaAs barrier is studied using temperature-dependent photoluminescence. The abnormal enhancement of the photoluminescence of the QDs in the layer with a larger amount of coverage at 110K is observed, which can be explained by considering the resonant Förster energy transfer between the wetting layer states at elevated temperatures.
Effect of Different Substrate Temperature on Phosphorus-Doped ZnO Thin Films Prepared by PLD on Sapphire Substrates
ZHAO Zi-Wen, HU Li-Zhong, ZHANG He-Qiu, SUN Jing-Chang, BIAN Ji-Ming, LIANG Hong-Wei, HUO Bing-Zhi, YU Dong-Qi, CHEN Xi, FU Qiang
Chin. Phys. Lett. 2009, 26 (5): 057305 .   DOI: 10.1088/0256-307X/26/5/057305
Abstract   PDF(pc) (616KB) ( 677 )
Phosphorus-doped ZnO (ZnO:P) thin films are deposited on a c-plane sapphire in oxygen at 350°C, 450°C, 550°C and 650°C, respectively, by pulsed laser deposition (PLD), then all the ZnO:P samples are annealed at 650°C in oxygen with a pressure of 1×105 Pa. X-ray diffraction measurements indicate that the crystalline quality of the ZnO:P thin films is improved with the increasing substrate temperature from 350°C to 550°C. With a further increase of the deposition temperature, the crystalline quality of the ZnO:P sample is degraded. The measurements of low-temperature photoluminescence spectra demonstrate that the samples deposited at the substrate temperatures of 350°C and 450°C show a strong acceptor-bound exciton (A0X) emission. The electrical properties of ZnO:P films strongly depend on the deposition temperature. The ZnO:P samples deposited at 350°C and 450°C exhibit p-type conductivity. The p-type ZnO:P film deposited at 450°C shows a resistivity of 1.846Ω&#12539;cm and a relatively high hole concentration of 5.100×1017 cm-3 at room temperature.
Influences of Bi2O3/V2O5 Additives on the Microstructure and Magnetic Properties of Lithium Ferrite
SU Hua, ZHANG Huai-Wu, TANG Xiao-Li, JING Yu-Lan, ZHONG Zhi-Yong
Chin. Phys. Lett. 2009, 26 (5): 057501 .   DOI: 10.1088/0256-307X/26/5/057501
Abstract   PDF(pc) (973KB) ( 703 )
Lithium ferrite materials with different concentrations of Bi2O3 and V2O5 additives are prepared by the conventional ceramic technique. The x-ray diffraction analysis proves that the additives do not affect the final crystal phase of the lithium ferrite in our testing range. Both Bi2O3 and V2O5 additives could promote densification and lower sintering temperature of the lithium ferrite. The average grain size first increases, and then gradually
decreases with the Bi2O3 content. The maximal grain size appears with 0.25wt% Bi2O3. The average grain size first increases, and then is kept almost unchanged with the V2O5 content. The maximal average grain size of the samples with V2O5 additive is much smaller than that of the samples with Bi2O3 additive. Furthermore, the V2O5 additive more easily enters the crystal lattice of the lithium ferrite than the Bi2O3 additive. These characteristics evidently affect the magnetic properties, such as saturation flux density, ratio of remanence Br to saturation flux density Bs, and coercive force of the lithium ferrite. The mechanisms involved are discussed.
Enhanced Magnetoresistance of (La0.67Ca0.33MnO3) Composites Coated byZn0.95Co0.05O
ZHUANG Bin, XU Yan, LAI Heng, HUANG Zhi-Gao, CHEN Shui-Yuan, LIN Ying-Bin, LI Shang-Dong, LAI Fa-Chun
Chin. Phys. Lett. 2009, 26 (5): 057502 .   DOI: 10.1088/0256-307X/26/5/057502
Abstract   PDF(pc) (458KB) ( 447 )
La0.7Ca0.3MnO3:xZn0.95Co0.05O (x = 0.0, 0.05, 0.1, 0.15 mol) composites are prepared by a sol-gel process. X-ray diffraction and energy diffraction spectroscopy reveal that there is no evidence of a reaction between the La0.7Ca0.3MnO3(LCMO) and Zn0.95Co0.05O (ZCO). Magnetization M, Curie temperature TC and metal-insulator transition temperatures Tp are observed to decrease with increasing ZCO content. Compared with x = 0.0, a great enhancement in the magnetoresistance (MR) is observed at around TC for x = 0.05, 0.10, 0.15. Based on the tunneling MR and percolation models, this great change of MR is well explained.
Effect of Zr Addition on Glass-Forming Ability and Magnetic Properties of Fe-Nd-Al-B Alloys Prepared by Suction Casting
BAI Qin, XU Hui, TAN Xiao-Hua, MENG Tao
Chin. Phys. Lett. 2009, 26 (5): 057503 .   DOI: 10.1088/0256-307X/26/5/057503
Abstract   PDF(pc) (776KB) ( 389 )

The microstructure and magnetic behaviors of the Fe-Nd-Al-B alloys prepared by suction casting with zirconium addition are investigated. With the small amount of zirconium addition, the magnetic properties of the alloys change from hard magnetic property to soft magnetic property. The proper addition of Zr (6%) not only improves the glass forming ability, but also suppresses the crystallization. From the scanning electron microscopy of the [(Fe0.53Nd0.37Al0.10)0.96B0.04]94Zr6 alloy and the local average elemental compositions determined using energy dispersive spectroscopy analysis, the amorphous phase with a composition of Fe47Nd38Al12Zr3 in the alloy can be observed. The bulk amorphous Fe47Nd38Al12Zr3 alloy is prepared by suction casting exhibiting good glass-forming ability and soft magnetic behavior.

Electromagnetic Parameters Model and Microwave Absorption for Composite Coatings Containing Magnetic Particles
HUANG Yao-Qing, HOU Zhi-Ling, SONG Wei-Li, YUAN Jie, CAO Mao-Sheng
Chin. Phys. Lett. 2009, 26 (5): 057701 .   DOI: 10.1088/0256-307X/26/5/057701
Abstract   PDF(pc) (412KB) ( 706 )
Considering the eddy current effect of the magnetic metal particles in a high frequency electromagnetic field, we extend the Maxwell-Garnett law by introducing the eddy-effect parameter A which is as functions of the radius, permeability and electric conductivity of the metal particle medium. It is obvious that the computational result agrees with the experiment, which indicates that the extended Maxwell-Garnett law can be used to predict the effective electromagnetic parameters of a dilute metal-insulator composite medium in a high-frequency electromagnetic field.
Modeling and Computing Example for Effective Electromagnetic Parameters of Multiphase Composite Media
SONG Wei-Li, YUAN Jie, HOU Zhi-Ling, CAO Mao-Sheng
Chin. Phys. Lett. 2009, 26 (5): 057702 .   DOI: 10.1088/0256-307X/26/5/057702
Abstract   PDF(pc) (1042KB) ( 467 )
A method using strong fluctuation theory (SFT) to compute the effective electromagnetic parameters of multiphase composite media, and common materials used to design radar-absorbing materials, is demonstrated. The effective electromagnetic parameters of ultrafine carbonyl-iron (DT-50) and fiber fabric, which are both multiphase composite media and represent coated and structured radar absorbing materials, respectively, are investigated, and the corresponding equations of electromagnetic parameters by using the SFT are attained. Moreover, we design a program to simplify the solutions, and the results are discussed.
Focusing of a Flat Left-Handed Metamaterial Lens in a Heterogeneous and Lossy Medium
WANG Gang, FANG Jie-Ran, WANG Hong-Jin
Chin. Phys. Lett. 2009, 26 (5): 057801 .   DOI: 10.1088/0256-307X/26/5/057801
Abstract   PDF(pc) (401KB) ( 430 )
For applications such as near-field target detection and tumor hyperthermia with a flat left-handed metamaterial (LHM) lens, a microwave will be focused in the heterogeneous and lossy medium. Different from the focusing of a flat LHM lens in vacuum as reported in most previous studies, the medium loss and heterogeneity will affect the focusing performance of the LHM lens. Numerical simulations indicate that the medium loss will degrade the focusing resolution, while the heterogeneity of random variability within ±30% will affect the focusing resolution to a limited extent. Both the loss and heterogeneity of the medium will shift the focal point away from the image plane. When focusing in a medium with different permittivity values, an LHM lens will also have different focusing resolutions due to different electric thicknesses.
Luminescence Properties of Nanostructure ZnO-Covered Carbon Fibers Prepared by Thermal Oxidation
ZENG Jun, WANG Sen, TAO Peng, HUA Wei, XU Jin-Cheng
Chin. Phys. Lett. 2009, 26 (5): 057802 .   DOI: 10.1088/0256-307X/26/5/057802
Abstract   PDF(pc) (769KB) ( 569 )
We report on ZnO nanosheets and nanorods synthesized by thermal oxidation of zinc films deposited on carbon fiber surfaces. The structure and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectrum. An orange-red emission around 683nm is found in the PL spectrum when the sample prepars at 400°C for four hours in air. With annealing temperature increasing from 400°C to 500°C, the blue shift is observed.
Monomer Adsorption-Desorption Processes
KE Jian-Hong, LIN Zhen-Quan, CHEN Xiao-Shuang
Chin. Phys. Lett. 2009, 26 (5): 058201 .   DOI: 10.1088/0256-307X/26/5/058201
Abstract   PDF(pc) (310KB) ( 397 )
We propose an adsorption-desorption model for a deposit growth system, in which the adsorption and desorption of particles coexist. By means of the generalized rate equation we investigate the cluster (island) size distribution in the dynamic equilibrium state. The results show that the evolution behaviour of the system depends crucially on the details of the rate kernels. The cluster size distribution can take the scale-free power-law form in some cases, while it grows exponentially with size in other cases.
An Anomalous Gain Mechanism in GaN Schottky Barrier Ultraviolet Photodetectors
ZHAO De-Gang, JIANG De-Sheng, LIU Zong-Shun, ZHU Jian-Jun, WANG Hui, ZHANG Shu-Ming, YANG Hui,
Chin. Phys. Lett. 2009, 26 (5): 058501 .   DOI: 10.1088/0256-307X/26/5/058501
Abstract   PDF(pc) (365KB) ( 468 )
The gain mechanism in GaN Schottky barrier ultraviolet photodetectors is investigated by focused light beam. When the incident light illuminates the central region of the Schottky contact electrode, the responsivity changes very little with the increase of reverse bias voltage. However, when the incident light illuminates the edge region of the electrode, the responsivity increases remarkably with the increase of reverse bias voltage, and the corresponding quantum efficiency could be even higher than 100%. It is proposed that the surface states near the edge of the electrode may lead to a reduction of effective Schottky barrier height and an enhancement of electron injection, resulting in the anomalous gain.
Evolutionary Games on Weighted Newman-Watts Small-World Networks
DU Wen-Bo, CAO Xian-Bin, ZHAO Lin, ZHOU Hong
Chin. Phys. Lett. 2009, 26 (5): 058701 .   DOI: 10.1088/0256-307X/26/5/058701
Abstract   PDF(pc) (2851KB) ( 527 )
We investigate the evolutionary prisoner's dilemma game (PDG) on weighted Newman-Watts (NW) networks. In weighted NW networks, the link weight wij is assigned to the link between the nodes i and j as: wij= (ki&#12539;kj)β, where ki(kj) is the degree of node i(j) and β represents the strength of the correlations. Obviously, the link weight can be tuned by only one parameter β. We focus on the cooperative behavior and wealth distribution in the system. Simulation results show that the cooperator frequency is promoted by a large range of β and there is a minimal cooperation frequency around β=-1. Moreover, we also employ the Gini coefficient to study the wealth distribution in the population. Numerical results show that the Gini coefficient reaches its minimum when β≈-1. Our work may be helpful in understanding the emergence of cooperation and unequal wealth distribution in society.
Uniqueness is Important in Competition
FENG Ai-Xia, XU Xiu-Lian, HE Da-Ren
Chin. Phys. Lett. 2009, 26 (5): 058901 .   DOI: 10.1088/0256-307X/26/5/058901
Abstract   PDF(pc) (296KB) ( 373 )
We propose a quantitative network description on the function of uniqueness in a competition system. Two statistical parameters, competition ability and uniqueness are defined, and their relationship in ordinary cases is analytically discussed. The cmpetition between Chinese regional universities is taken as an example. The empirical investigation results show that the uniqueness of a university is really important in competition. Also, uniqueness is very helpful in the promotion of the university overall quality.
Theoretical Studies on Defects of Kaolinite in Clays
HE Man-Chao, FANG Zhi-Jie, ZHANG Ping
Chin. Phys. Lett. 2009, 26 (5): 059101 .   DOI: 10.1088/0256-307X/26/5/059101
Abstract   PDF(pc) (369KB) ( 361 )
Using the first-principles methods, we study the formation energetics and charge doping properties of the extrinsic substitutional defects in kaolinite. Especially, we choose Be, Mg, Ca, Fe, Cr, Mn, Cu, Zn as extrinsic defects to substitute for Al atoms. By systematically calculating the impurity formation energies and transition energy levels, we find that all group-II defects introduce the relative shallow transition energy levels in kaolinite. Among them, MgAl has the shallowest transition energy level at 0.08eV above the valence band maximum. The transition-elemental defects FeAl, CrAl, and MnAl are found to have relative low formation energies, suggesting their easy formation in kaolinite under natural surrounding conditions. Our calculations show that the defects CuAl and ZnAl have the high formation energies and deep transition energy levels, which exclude the possibility of their formation in natural kaolinite.
Dynamic Processes of Cross-Tail Current in the Near-Earth Magnetotail
LU Xing-Qiang, MA Zhi-Wei,
Chin. Phys. Lett. 2009, 26 (5): 059401 .   DOI: 10.1088/0256-307X/26/5/059401
Abstract   PDF(pc) (291KB) ( 493 )
Current dynamic processes in realistic magnetotail geometry are studied by Hall magnetohydrodynamic (MHD) simulations under various driven conditions and Hall effects. Associated with the external driving force, a thin current sheet with a broad extent is built up in the near-Earth magnetotail. The time evolution for the formation of the current sheet comprises two phases: slow growth and a fast impulsive phase before the near-Earth disruption of the current sheet resulting from the fast magnetic reconnection. The simulation results indicate that as the external driving force increases, the site and the tailward speed of the near-Earth current disruption region are closer to the Earth and faster, respectively. Whether the near-Earth disruption of the current sheet takes place or not is mainly controlled by Hall effects. It is found that there is no sudden disruption of the current sheet in the near-Earth region if the ion inertial length is below di=0.04.
Bounce-averaged Pitch-angle Diffusion by Electromagnetic Ion Cyclotron Waves in Multi-ion Plasmas
XIAO Fu-Liang, TIAN Tian, CHEN Liang-Xu
Chin. Phys. Lett. 2009, 26 (5): 059402 .   DOI: 10.1088/0256-307X/26/5/059402
Abstract   PDF(pc) (296KB) ( 364 )
We present a study on the gyroresonant interaction between electromagnetic ion cyclotron waves and ring current particles in multi-ion (H+, He+, and O+) plasmas. We provide a first evaluation of the bounce-averaged pitch angle diffusion coefficient <Dαα> for three typical energies of 50, 100 and 150keV at L≈3.5, the heart of the symmetrical ring current. We show that in the H+-band and He+-band, <Dαα> can approach ~10-4s-1 for ion H+, and ~5× 10-5s-1 for ion He+; meanwhile, in the O+-band, <Dαα> can reach ~10-5s-1 for ions He+ and O+. The results above show that the EMIC wave can efficiently produce precipitation loss of energetic (~100keV) ions (H+, He+ and even O+), and such a wave tends to be a serious candidate responsible for the ring current decay.
Vacuum Outer-Gap Structure in Pulsar Outer Magnetospheres
LIN Gui-Fang, ZHANG Li
Chin. Phys. Lett. 2009, 26 (5): 059501 .   DOI: 10.1088/0256-307X/26/5/059501
Abstract   PDF(pc) (278KB) ( 390 )
We study the vacuum outer-gap structure in the outer magnetosphere of rotation-powered pulsars by considering the limit of trans-field height through a pair production process. In this case, the trans-field height is limited by the photon-photon pair production process and the outer boundary of the outer gap can be extended outside the light cylinder. By solving self-consistently the Poisson equation for electrical potential and the Boltzmann equations of electrons/positrons and γ-rays in a vacuum outer gap for the parameters of Vela pulsar, we obtain an approximate geometry of the outer gap, i.e. the trans-field height is limited by the pair-production process and increases with the radial distance to the star and the width of the outer gap starts at the inner boundary (near the null charge surface) and ends at the outer boundary which locates inside or outside the light cylinder depending on the inclination angle.
Evolving into Magnetars from Normal Pulsars with a Low Braking Index
CHEN Wen-Cong
Chin. Phys. Lett. 2009, 26 (5): 059701 .   DOI: 10.1088/0256-307X/26/5/059701
Abstract   PDF(pc) (221KB) ( 527 )
Anomalous x-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are believed to be candidates for magnetars, and they are powered by the decay of ultra-strong magnetic fields of >1014G. From the modified spin-down relation of pulsars &#12539;P∝P2-n, we find that the Vela pulsar would evolve into the classes of magnetars under some assumptions that pulsars lose their rotational energy only by magnetic dipole radiation and the braking index is a constant. Our rough calculation indicates that only pulsars with n~1.3-1.6 can evolve into magnetars. Pulsars like Vela with a low braking index may be the progenitors of AXPs and SGRs. Regarding the mechanism evolved into magnetars, we suggest that pulsars' surface magnetic field component may be increased by frequent glitches.
Comment on ``Ported from Self-Similar Analytic Solutions of Ginzburg-Landau Equation with Varying Coefficients''
WU Lei
Chin. Phys. Lett. 2009, 26 (5): 059901 .   DOI: 10.1088/0256-307X/26/5/059901
Abstract   PDF(pc) (201KB) ( 435 )
Reply to the ``Comment on `Ported from Self-Similar Analytic Solutions of Ginzburg-Landau Equation with Varying Coefficients' ''
FENG Jie, XU Wen-Cheng, LI Shu-Xian, LIU Wei-Ci, LIU Song-Hao
Chin. Phys. Lett. 2009, 26 (5): 059902 .   DOI: 10.1088/0256-307X/26/5/059902
Abstract   PDF(pc) (215KB) ( 370 )
Comment on ``Electrical Conductivity and Current-Voltage Characteristics of Individual Conducting Polymer PEDOT Nanowires''
P. Ohlckers P. Pipinys
Chin. Phys. Lett. 2009, 26 (5): 059903 .   DOI: 10.1088/0256-307X/26/5/059903
Abstract   PDF(pc) (192KB) ( 434 )
Reply to ``Comment on `Electrical Conductivity and Current-Voltage Characteristics of Individual Conducting Polymer PEDOT Nanowires'''
Chin. Phys. Lett. 2009, 26 (5): 059904 .   DOI: 10.1088/0256-307X/26/5/059904
Abstract   PDF(pc) (167KB) ( 457 )
79 articles